In a controlled, prospective trial, the effects of giving ferrous sulphate 50 mg daily to 76 pregnant women was compared with giving ferrous sulphate 50 mg daily plus folic acid 0.5 mg daily to 82 women in 12 general practices in South-east England.No differences in obstetric complications were found between the two groups, although the evidence of some of the listed complications may be too rare for detection in a sample of patients of this size.